Yes, in my case, but also fastmail includes unlimited @fastmail.com email addresses, delivered to your normal inbox, and can even be generated on the fly by password managers like Bitwarden.
On aliases, the limit is 600. Maybe you mean the recently added masked emails. The limit on those is not documented, but rumor says it's 1,000.[1]
[1] https://www.reddit.com/r/fastmail/comments/t68eiw/comment/hz...